Contact lens, method for producing same, and pack for storage and maintenance of a contact lens

ABSTRACT

A contact lens ( 4 ) comprises a solid component capable of imparting shape and structure to said lens, and a liquid component, at least partially contained in the solid component, capable of favoring the compatibility between said lens and the eye of a user of said lens, wherein the liquid component comprises a solution capable of being used as a lachrymal substitute.

RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 11/814,556, filed onJul. 23, 2007, which is a §371 national stage application ofPCT/IT2006/000067, filed on Feb. 9, 2006, now U.S. Pat. No. 7,726,809.

TECHNICAL FIELD

The present invention relates to a method of preserving a contact lens,using a liquid comprising an effective amount of galactoxyloglucanextracted from tamarind seed as a preserving liquid for the contactlens.

TECHNOLOGICAL BACKGROUND

It is known that contact lenses, whether they are cosmetic orcorrective, are widely used among the population. Among these,particular importance is given to contact lenses of the soft type,which, compared with the other types of lenses (rigid or semi-rigid)provide greater comfort in use.

This advantageous characteristic is provided by the high hydrophiliccapacity of the lens which, containing a substantial percentage ofwater, permits greater compatibility between the lens and the eye, inaddition to a greater deformability of the lens which allows it to adaptbetter to the surface of the eye.

Soft contact lenses are conventionally produced by means of a methodwhich provides for a first step of obtaining a dry semi-manufacturedproduct of lenticular shape and made of polymeric material, which may inturn be obtained by the polymerization of a monomer directly in a die(moulding technique), or by turning a disc of already polymerizedmaterial (turning technique).

Independently of the technique used for its preparation, the drysemi-manufactured product is then hydrated by immersion in a salinesolution (known as a physiological solution) composed of around 1% byweight of sodium chloride in water. The polymeric material used istypically endowed with optimum hydrophilic properties, and is normally apolymeric mixture based on HEMA, so that a substantial amount of salinesolution, between 25% and 75%, is absorbed in the dry semi-manufacturedproduct.

The absorption of the liquid component, besides imparting to the lensthe above-mentioned characteristics of compatibility and softness, alsoincludes physical expansion of the dry semi-manufactured product, bothradial and linear, thus determining both the final dimensions of thecontact lens, and its optical properties.

The contact lens thus obtained thus comprises a solid component,defining the structural portion of the lens and composed of thepolymeric material, and also a liquid component, composed of the salinesolution, distributed almost uniformly in the solid component.

The marketing of the contact lens provides for the preparation ofsuitable packs, produced for example in the form of blister packs, inwhich the lenses are stored and maintained for the entire period betweenthe end of the process of manufacturing same, and the first use thereofby a user.

The packs must therefore be arranged to maintain unaltered over time themechanical, optical and dimensional characteristics of the lenses.

To this end, the packs typically comprise a support defining a containerwhich is filled, at least partially, with physiological solution, inwhich the contact lens, in its turn, is immersed. The container isfurther conveniently closed by a membrane, generally constituted by athin metallic sheet (known in the field as a “foil”), subsequentlyremovable by the user in order to extract the lens from the container.

It is known that one of the major drawbacks arising from the use ofcontact lenses is represented by the sensation of ocular dryness, causedby the reduction or by the breakdown of the lachrymal film whichsurrounds and protects the cornea. This typically involves a sensationof discomfort and irritation which frequently forces the user to removethe lenses and which, in the long term, may also lead to changes in thelachrymal function and to other pathological disfunctions at the expenseof the eye (such as, for example, corneal or conjunctival inflammation).

Also owing to this drawback, many persons are capable of wearing thecontact lenses only for a very limited time or are even prevented fromdoing so.

In order to overcome this drawback, at least in part, various technicalsolutions have been developed and proposed.

A first of these solutions, for the formation of the solid component,provides for the use of polymers and/or copolymers having the highestpossible hydrophilic properties. Such polymers and/or copolymers may beused for producing the entire solid component of the lens, or only as anouter coating of same. The use of such polymers, however, has a negativeeffect on the overall costs of production, but without succeeding inproviding resolutory advantages with regard to the above-mentioneddrawback. Moreover, such use may also turn out to be counter-productivein the case where the lens remains in the eye for a prolonged period,since the greater the amount of water released by the contact lens, thegreater the variation in the dimensions thereof, with potential negativerepercussions on its optical properties.

A second known solution is provided by the use of external solutions,known generically and overall as “lachrymal substitutes” (“artificialtears”). These latter are aqueous solutions comprising substances,generally polymers, the overall properties of which tend to reproduce,as far as possible, the properties of the natural lachrymal liquid.

In order that an aqueous solution can be defined as a lachrymalsubstitute, it must possess particular chemico-physical and rheologicalcharacteristics and bio-compatibility. In particular, specific and highvisco-elastic and hydrophilic properties are required, as well asmuco-adhesive properties (in order to remain attached for as long aspossible to the mucinic component of the lachrymal film), mucomimeticproperties (for simulating in the best possible manner the behaviour ofthe lachrymal film) and the ability to bathe the cornea, in addition,obviously, to general compatibility with the tissues of the eye.

The use of lachrymal substitutes provides for their addition as dropsdirectly on to the eye to which the contact lens is fitted, so that theneed to have recourse to this expedient is a not very pleasingeventuality to many people, without considering the furtherinconvenience of having to carry phials or containers with one.Moreover, the beneficial effect of the lachrymal substitutes is verylimited over time, so that it is often necessary to have recourse tothem several times a day and in all kinds of places.

In certain cases, provision is also made for the application of thelachrymal substitute to take place directly on the lens, both when wornand prior to its being fitted, but this expedient does not substantiallymodify the picture described above. In fact, the absorption of thelachrymal substitute into the lens is limited to its outermost surfacelayers, and is therefore retained in very small amounts and thus with abeneficial effect necessarily limited over time.

The wider view of the technical field of reference of the invention iscompleted by contact lenses used as vehicles for the administrationthrough the eye of drugs for therapeutic use. Such lenses, known also as“ophthalmic dressings”, are typically contact lenses obtained in a quiteconventional manner, to which are then added one or more drops of thedrug to be administered. The effect of release of the drug has, however,a very limited duration. Some solutions for contact lenses are alsoknown for use as ophthalmic dressings, in which an endeavour has beenmade to increase the duration of the release of the drug. One of thesesolutions provides for the interposition of a support soaked in thesubstance to be administered between a pair of contact lenses.

DESCRIPTION OF THE INVENTION

The problem underlying the present invention is that of providing acontact lens, a method for producing same, and also a pack for thestorage and maintenance of contact lenses structurally and functionallydesigned to remedy the limits described above with reference to theprior art cited.

This problem is solved by the present invention by means of a contactlens, a method for producing same, and a pack for its storage andmaintenance, provided in accordance with the following claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics of the invention will become clearer from thefollowing detailed description of a preferred exemplary embodimentthereof, illustrated by way of non-limiting example with reference tothe appended drawings, in which:

FIG. 1 is a diagrammatic perspective view of a contact lens producedaccording to the present invention,

FIG. 2 is a diagrammatic perspective view of a pack for the storage andmaintenance of the contact lens of FIG. 1.

PREFERRED WAY OF IMPLEMENTING THE INVENTION

In the appended drawings, a contact lens produced according to thepresent invention is designated as a whole by 4.

The contact lens 4 is a lens of the soft type and may be of any knowntype, for cosmetic or corrective use, coloured or transparent, withoutthereby influencing to any significant extent the innovative aspects ofthe present invention.

The lens 4 is produced according to the following method.

In a first step, according to techniques that are quite conventional perse (by moulding or turning), a dry semi-manufactured product ofpolymeric material is produced, capable of imparting to the lens thestructure and final configuration. The dry semi-manufactured product maybe obtained from a polymeric mixture based on HEMA or from any otherpolymer or copolymer suitable for this purpose and normally used in thefield.

In a subsequent preparation step, the dry semi-manufactured product isthen hydrated by immersion in an aqueous solution, suitably agitated, sothat into the solid component a liquid component is substantiallyuniformly absorbed, which favours comfortable use of the lens andtherefore its compatibility with the eye of a user in which it isintended to be worn.

At the end of the hydration step, the lens 4 is then ready to bepackaged and afterwards sterilised by means of treatment in an autoclaveat around 120° C. for a period of around 20 minutes.

FIG. 2 illustrates a pack for the storage and maintenance of the lens 4,indicated as a whole by 1. The pack 1 comprises a support 2, sheet-likeand made for example of plastics material, configured in such a way asto define a container 3, inside which the lens 4 is immersed in amaintenance liquid 5.

The pack 1 also comprises a membrane 6 (so-called foil) coupled, forexample by means of heat-welding, on a peripheral edge of the support 2so as to seal the container 3 and prevent the escape of the lens 4 or ofthe liquid 5. The coupling between membrane 6 and support 2 is effectedin such a way as to guarantee the closure of the container 3, permittingat the same time its manual removal by the user on deciding to extractthe lens from the pack 1.

For greater clarity, in FIG. 2, the membrane 6 is shown in a partiallylifted position.

According to a first aspect of the invention, the aqueous solution inwhich the dry semi-manufactured product is immersed for the hydrationtreatment is a solution capable of being used as a lachrymal substitute.

The contact lens thus obtained therefore comprises, like a conventionallens, a solid component, composed substantially of the polymericmaterial, and a liquid component distributed substantially uniformly inthe solid component in which the liquid component is a lachrymalsubstitute.

The fraction of liquid component present in the contact lens is between25% and 75%.

The lachrymal substitute used in the present invention is constituted byan aqueous solution comprising an effective amount of one or morepolymers selected from the group consisting of polyvinyl alcohols andtheir derivatives, polysaccharides and their derivatives, and alsocellulose derivatives. Preferably, the lachrymal substitute comprises,in addition to one or more polymers identified above, an effectiveamount of metallic ions, usually present also in natural lachrymalliquid, such as calcium, potassium and/or magnesium ions.

The polymers present in the lachrymal substitute may have a linear,branched or crosslinked structure, preferably such as to reproduce andsimulate the structure of the mucinic cells present in natural lachrymalliquid.

In particular, the preferred lachrymal substitutes comprisepolysaccharides and their derivatives, such as, for example, dextran,galactoxyloglucan, hyaluronic acid or their derivatives.

In an absolutely preferred manner, the lachrymal substitute comprises aneffective amount of a galactoxyloglucan extracted from tamarind seed(TSP). This polysaccharide has a molecular weight of around 600 KDalton,optimum hydrophilic properties and a branched molecular structure whichrenders it particularly similar to the natural mucinic cells andtherefore able to bond effectively with the proteins of the mucouslayer.

TSP also has other characteristics which cause it to be particularlypreferred among the other compounds used as active principles inlachrymal substitutes.

A first of these characteristics is provided by its considerable heatresistance, which allows TSP to resist, without altering significantly,the conditions for sterilisation of the lens in an autoclave (around120° C. for about 20 minutes).

A second advantageous characteristic is provided by the capacity of TSPfor blocking ultraviolet radiation (UV), which makes it possible to savean additive commonly used in contact lenses. Not only this, the slow andgradual release of the TSP-based solution in the eye allows protectionfrom UV rays on an ocular surface greater than that strictly covered bythe lens.

A third characteristic exhibited by the TSP-based lachrymal substituteswhen used in a contact lens according to the present invention lies inthe fact that, surprisingly, their behaviour within the polymerconstituting the solid component is, in terms of swelling of the latter,entirely comparable to that of a normal physiological solution,imparting in the hydration phase substantially the same variations tothe dry semi-manufactured product both in the radial direction and inthe linear direction. This makes it possible to maintain substantiallyunvaried the parameters currently in use for the sizing of the drysemi-manufactured product. According to various studies, other commonlachrymal substitutes tend to swell the more common polymeric material(HEMA) in a different manner from the physiological solution, such thattheir use as liquid component of the lens according to the presentinvention involves revision of the sizing of the dry semi-manufacturedproduct and therefore of the machining process.

A fourth characteristic, particularly significant in the application ofTSP in a lens according to the present invention, is provided by itsoptimum capacity, entirely unexpected, of remaining for a long timewithin the polymer constituting the solid component of the contact lens4. This property allows the lens 4 to retain the lachrymal substitutefor a substantially longer period within the solid component, so as toprolong the beneficial effect thereof.

The TSP-based aqueous solution may comprise from 0.1% to 1% by weight ofTSP, and preferably comprises 0.2% thereof. In addition to the TSP, thesolution may also comprise a buffering agent and a disinfecting agent.

A second lachrymal substitute that can be used for the production ofcontact lenses according to the present invention is constituted by anaqueous solution comprising an effective amount of sodium hyaluronate.In particular, the aqueous solution may comprise sodium hyaluronate inan amount of between 0.1% and 0.3% by weight, preferably around 0.2%, asurfactant, for example in an amount of around 0.0015%, a disinfectingagent, for example disodium EDTA, in an amount of around 0.1%, abuffering agent such as to maintain an overall pH of around 7.3-7.4, andalso, optionally, sodium chloride in an amount of around 0.9%.

Owing to the presence of the lachrymal substitute in its liquidcomponent, the fitting of the contact lens according to the invention ismuch more comfortable, significantly reducing the problems of asensation of ocular dryness normally deriving from the use ofconventional contact lenses.

The lachrymal substitute, in fact, is slowly released into the eye,developing a lubricating, hydrating and re-epithelising action whichrestores the lachrymal film, thus preventing, or at least greatlylimiting, the occurrence of the problems of ocular dryness.

It has further been found that the speed of release of the lachrymalsubstitute depends on the temperature, determining a greater speed ofrelease when the lens is worn by the user (to which an internaltemperature of around 35° C. may be attributed), compared with when thelens is kept in the appropriate containers (temperature normally between18° C. and 25° C.).

The contact lenses according to the invention may be produced so as tohave to be replaced monthly or more frequently, for example daily,weekly or twice-weekly, depending on the polymeric material preselectedand on its characteristics of retention of the liquid component.

Preferably, the contact lens is of the weekly or daily replacement type.

EXAMPLE 1

A soft contact lens was produced from a dry semi-manufactured productobtained by moulding from a polymeric mixture based on HEMA, and whichwas then hydrated in an aqueous solution comprising 0.2% of TSP, around2% of mannitol and around 2% of monobasic and dibasic sodium phosphate.

EXAMPLE 2

A soft contact lens was produced by hydrating a dry semi-manufacturedproduct, obtained in an analogous manner to that of example 1, in anaqueous solution comprising 0.2% of sodium hyaluronate, around 0.0015%of a surfactant, 0.1% of disodium EDTA as disinfecting agent, and abuffering agent based on sodium phosphate.

The contact lenses obtained from examples 1 and 2 were then subjected tosome tests.

As a preliminary, the distribution of the lachrymal substitute withinthe lens was evaluated. These preliminary analyses were conducted bysectioning the lens into a representative number of samples, colorationwith suitable dyes reacting with the hyaluronate and the TSP (forexample saframin and toluidine blue) and subsequent observation of theintensity of the coloration with an optical microscope.

These analyses showed that the lenses obtained according to example 1and example 2 exhibit a substantially uniform distribution of sodiumhyaluronate and TSP within the lens, over its entire thickness.

The lenses of examples 1 and 2 were then tested on various subjects inorder to check the wearability and the degree of comfort during usecompared with conventional lenses, hydrated with physiological solution.

Both the contact lenses tested provided good results in terms of comfortof fitting on the eye and of duration of time before the onset of thefirst symptoms of ocular dryness, far better than those obtained by theconventional contact lenses.

The tests also showed that the lens hydrated with the TSP-basedlachrymal substitute (example 1) is more effective than that obtainedwith the lachrymal substitute based on sodium hyaluronate (example 2),maintaining its capacity for preventing ocular dryness for a longertime.

According to another aspect of the present invention, the maintenanceliquid 5 in which the lens 4 is immersed in the pack 1 is also alachrymal substitute and, preferably, is of the same type as thelachrymal substitute used in the step of hydration of the drysemi-manufactured product.

In this way, the possibility is avoided of loss of lachrymal substitutepresent in the contact lens, though in any case limited to the outermostsurface layers, because of substitution with a less suitable maintenanceliquid, for example the usual physiological solution.

According to another aspect of the present invention, the packaging of asoft contact lens using as maintenance liquid a solution capable ofbeing used as a lachrymal substitute may also be applied to soft contactlenses of conventional type, hydrated with physiological solution.

In this case, in fact, the immersion of the finished contact lens in amaintenance liquid based on a lachrymal substitute means that at theoutermost surface layers of the lens, owing to the normal process ofexchange with the actual inner liquid component, some fraction oflachrymal substitute is absorbed. In this way, when the lens isextracted from the container of the pack 1 in order to be worn by auser, it has, at least in its outermost layers, an amount of lachrymalsubstitute sufficient to ensure more comfortable use thereof, even formany hours, compared with the conventional lenses hydrated andmaintained in physiological solution.

The duration of the beneficial effect will certainly be limited withrespect to the case described previously in which the lens is hydratedwith a lachrymal substitute, yet it is not insignificant.

In a particularly preferred manner, the lachrymal substitute used asmaintenance liquid in a pack for the storage and maintenance of acontact lens of conventional type, that is, hydrated with physiologicalsolution, is based on TSP. Owing, in fact, to the surprising andunexpected affinity of same with the polymer constituting the solidcomponent of the lens, the beneficial effect deriving from its presenceon the surface of the lens once removed from the pack in order to befitted onto the eye, persists for a decidedly longer time compared withthe other lachrymal substitutes.

Preferably, the contact lens will be of the frequent replacement type,for example weekly or more frequently, and, even more preferably, inorder to benefit fully from the advantages offered by this aspect of theinvention, the contact lens will be of the disposable type, for dailyreplacement.

According to a further aspect of the invention, provision is also madefor the possibility of preserving and optionally disinfecting thecontact lenses obtained according to the present invention with apreserving solution. Solutions of this type are used for preserving thelenses between one application and another, once removed from thestorage and maintenance pack in which they are sold.

Preferably, the preserving solution comprises an effective amount of thepolymer already present in the liquid component of the contact lens.

For example, in the case of a preserving solution for a contact lenscomprising a TSP-based lachrymal substitute, such a preserving solutionfor the contact lenses will comprise a buffered physiological solutionand an effective amount of TSP.

Optionally, provision is made for the preserving solution to be able tohave disinfectant properties, so that it may also comprise adisinfecting agent from among those normally used in the field, forexample sodium EDTA.

The presence in the preserving solution for the contact lenses of thepolymer which is the basis of the lachrymal substitute in which the lensitself is soaked, makes it possible, particularly in the case of lenseswith a low, for example monthly, frequency of replacement, to prolongover time the efficiency of the contact lens according to the invention.In fact, with use, the lachrymal substitute present initially in thelens will tend to decrease and its preservation in a solution such asthat described above makes it possible, at least partially, to maintainin the lens an acceptable amount of the polymer which is the basis ofthe lachrymal substitute, prolonging its beneficial effect.

As in the case relating to the packaging of the contact lenses, thissolution for preserving the contact lenses may also be used for contactlenses obtained in a conventional manner.

The present invention therefore solves the problem mentioned above withreference to the prior art cited, offering at the same time numerousother advantages, including the fact of providing a contact lens whichmay be obtained by means of a simple and inexpensive production method.A further advantage of the invention is provided by the fact that thewearability of the contact lens is increased significantly, thus makingit particularly useful for use in notoriously unfavourable conditions,for example in work stations in front of monitors or television screens.

1. A method of preserving a contact lens, the method comprising:immersing a contact lens in an aqueous solution comprising from 0.1 to1% by weight of a tamarind seed galactoxyloglucan having a molecularweight of 600 kilodaltons.
 2. The method of claim 1, wherein the aqueoussolution further comprises a disinfecting agent.
 3. The method of claim1, wherein the aqueous solution comprises 0.2% by weight of the tamarindseed galactoxyloglucan having a molecular weight of 600 kilodaltons. 4.The method of claim 1, wherein the aqueous solution further comprisesabout 2% by weight of a buffering agent.
 5. The method of claim 4,wherein the buffering agent is a combination of monobasic sodiumphosphate and dibasic sodium phosphate.
 6. The method of claim 1,wherein the aqueous solution further comprises about 2% by weight ofmannitol.
 7. A method of preserving a contact lens, the methodcomprising: immersing a contact lens in an aqueous solution comprising:from 0.1 to 1% by weight of a tamarind seed galactoxyloglucan having amolecular weight of 600 kilodaltons; about 2% by weight of mannitol; andabout 2% by weight of a buffering agent, wherein the buffering agent isa combination of monobasic sodium phosphate and dibasic sodiumphosphate.
 8. The method of claim 7, wherein the aqueous solutioncomprises 0.2% by weight of the tamarind seed galactoxyloglucan having amolecular weight of 600 kilodaltons.